Coated woofer - why?

Coating a speaker will reduce the amplitude of cone break-up and the associated resonant behavior. Especially in the upper frequencies of the drivers range.

Those KEF drivers were coated with a doping compound called plastiflex, which did exactly that.

Smooth response and low coloration are the audible results.

Let me add, since coating the woofers was done by KEF as part of their construction, I am not sure you could call this a "mod".

Back in the days when i made my own speakers I used to do it to add mass to lower the FS (free air resonance) of the driver and to stiffen the cone.
The way it was done to have a nice ripple effect is to face the driver upwards paint it with thick coat of dust cap glue/Aquadhere (a clear drying wood glue) give it a 25hz sine wave single so it’s wobbling nicely, this gives the glue the ripple look while it sets, 20mins or so. 

Cheers George

You just can't help yourself, can you ebm...

An old (20+ years) speaker with multiple previous owners has a coated woofer - why would this mod be made? What are the implications for SQ? Speaker is a LS35A type with original KEF B110 woofer.

Let me add, that if you are in need of direct replacements, the company Falcon Acoustics, sells all replacement parts.

https://www.falconacoustics.co.uk/bbc-ls3-5a/falcon-ls3-5a-b110-drive-units.html  

It couldn’t hurt to think about replacing those old woofers. Surrounds, glue, etc tends to age.

Thanks guys, glad to have learned a bit today.  Wish I could have seen the post that was deleted, I am sure I missed out on a nasty clever bit of advice, hopefully it was a pun.  I was expecting a “cuz its cold” but ebm must have been much better.

Anyway, simonmoon, this was certainly a mod as other speakers of the same brand/type do not have this look, a glossy blackish kinda coating, and the owner mentions the coating.  

Trust me, you didn't miss a thing....

JBL did this back in the 70’s or maybe earlier with a coating called Aquaplas which I believe was like a silica based epoxy spray. Supposed to improve damping, making paper cones more rigid and probably, and historically proven to extend the cones life without the inherent dry rotting of old paper cones. I’ve got a pair of WX 4311s from the 70’s and the original woofer cones are still very firm and rigid. Also the treated accordion cloth surrounds were way ahead of their time. 

Btw this was the way Sonus Faber did the same FS (resonant frequency) lowering and stiffening of their bass cones on their stuningly magical sounding Extremas.

https://images.app.goo.gl/w9frGfkLN9dfrJoJ6

Cheers George

ScotchGard is used for waterproofing speaker cones that may be exposed to water and is not supposed to hurt the output. I have never seen this in person but that might have the same appearance you are describing.

thosb, I think as simmonmoon suggests it is time to replace those drivers.
Modifying drivers in the context of a speaker system without ample test equipment is a sketchy thing to do. As an example the coating added mass to the cone which changes the characteristics of the driver and then it's relationship to the crossover. God knows what that did to the speaker.
The LS 3/5A is a magic little loudspeaker. Why anyone would want to mess with it is beyond me.

Seas is coating some drivers with graphene now. Not sure what the benefit is, or if its just part of the "put graphene on everything" rage going on right now.